The present invention relates generally to a hydraulic control system used in an automatic transmission for a vehicle, and more particularly to a pressure control configuration for regulating line pressure in the hydraulic control system.
A conventional automatic transmission used in vehicles generally includes a multi-stage gear mechanism, a torque converter connected thereto, and a plurality of clutch elements actuated by hydraulic pressure for selecting one of the gears of the gear mechanism. A hydraulic control system for an automatic transmission operates by selectively supplying hydraulic pressure from a hydraulic pump to the clutch elements by a plurality of control valves such that shifting may be realized automatically according to the driving situation.
The hydraulic control system generally includes a hydraulic fluid source, a line pressure controller for regulating hydraulic pressure supplied from the fluid source to line pressure, and a hydraulic pressure distributor for determining a hydraulic flow path corresponding to the respective transmission speeds according to the hydraulic pressure from the shift controller and suitably distributing the operational pressure to each friction element.
In traditional automatic transmissions, the line pressure is usually maintained at two different levels while in the xe2x80x9cDrivexe2x80x9d position. The first pressure remains constant while in first and second gears, and depending on application is around 135 psi. When the transmission shifts from second to third, the pressure lowers to around 85 psi depending on the application. The pressure remains at that pressure as the transmission shifts to fourth gear.
It would be desirable to provide a transmission that had the ability to vary the line pressure according to an optimal running condition. For example, in some conditions it would be favorable to run the transmission at a lower pressure while in the higher gears. If a lower line pressure can be maintained without inducing clutch slip, the longevity of the transmission as well as the fuel economy of the vehicle would be increased. Similarly, it may be desired to increase the line pressure in a low gear situation where clutch holding torque capacity is needed. A variable pressure configuration would allow the transmission to operate at an optimal pressure according to the condition and avoid relying on two predetermined pressures.
It is an object of the present invention to provide a hydraulic control system for an automatic transmission including a planetary gear system having a plurality of clutch elements to alter the torque ratio of the transmission.
It is another object of the present invention to provide a line pressure control device for variably regulating hydraulic pressure supplied from the fluid source.
It is yet another object of the present invention to provide a line pressure regulating valve influenced by a solenoid which is in communication with the transmission control module which is using signals from the input and output sensors as well as engine throttle angle.
It is a further object of the present invention to provide a line pressure control device for regulating hydraulic pressure which provides increased fuel economy and transmission life.
It is still another object of the present invention to replace the multitude of parts comprising a traditional regulator valve with one single valve.
The present invention obtains these and other objects by providing a new configuration for a regulator valve in an automatic transmission. The configuration according to this invention includes a first fluid port communicating with the manual valve, a second fluid port communicating with the fluid pump and a third fluid port influenced by a solenoid communicating with the fluid pump. The solenoid is energized according to the desired line pressure needed for a given situation. The solenoid is actuated accordingly to achieve the lowest line pressure available avoiding clutch slip. By maintaining line pressure at an optimal level, the durability of the transmission components as well as the fuel efficiency of the vehicle is increased.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.